The present invention generally relates to communication over power lines and, more particularly, to providing both direct current power and digital communications simultaneously on the same wire for avionics and control systems in airborne vehicles and spacecraft.
Current airborne vehicle electronics—such as that which is used for military or commercial aircraft or satellites—are typically controlled through data quality wiring that connects the avionic units in digital networks. Data quality wiring, for example, may be twisted shielded pair wiring. Data communication in military aircraft is commonly achieved using communication as specified by military standard MIL-STD-1553, hereafter referred to as “1553 communication” , as known in the art, to link the avionics boxes, i.e. avionics units, together into digital networks. Airborne vehicle wiring can include hundreds of feet of wire. A small jet fighter, for example, may have 20 avionics systems that are connected to each other via a digital network. The data quality network wiring can add considerable amount of weight to an aircraft or to a spacecraft—such as a satellite. Weight and volume are critical design constraints for any aircraft or spacecraft, so that any weight and volume savings that can be achieved in the design of an aircraft or spacecraft—such as eliminating the weight of data quality network wiring, along with the spatial volume occupied by such wiring—can be an important benefit to the performance of the aircraft or spacecraft.
FIG. 1 shows a prior art example of network wiring and power lines for a system 100 that is typical for aircraft and spacecraft. System 100 may include a number of avionics units, or boxes, 102—such as avionic unit 102a, avionics unit 102b, and avionics unit 102c. An avionics unit may perform any of several functions important to an aircraft. Aircraft avionics are generally partitioned into subsystems such as RADAR, weapons, flight controls, displays, and so forth. The RADAR and flight instruments, for example, would be considered as components in separate subsystems. System 100 illustrates how communication may be achieved between different subsystems in an aircraft or spacecraft. Each avionics unit 102 may include host electronics 104 specific to some particular avionics function. For example, avionics unit 102a may include host electronics 104a for a sensor that may receive a radar signal, and avionics unit 102b may include host electronics 104b for a display such as a cockpit instrument panel display. Also, avionics unit 102c may include host electronics 104c, which may be, for example, a radio transmitter or receiver. In a more general context, host electronics 104 may include any digital device such as a computer microprocessor or a computer.
Avionics system 100 may require, for example, that host electronics 104a communicate that it has received the radar signal to host electronics 104b for display. Thus, host electronics 104a may provide data 108 to modem 106a. Modem 106a may modulate a signal 110 with data 108, for example, using pulse code modulation (PCM), phase shift keying (PSK), or frequency shift keying (FSK). Signal 110 may be transmitted over data quality wiring 112 of network 114. For example, wiring 112 may be twisted shielded pair wiring, as described above. Network 114 may use “1553 communication” , Ethernet protocol, or other protocol for routing signal 110 over bus 116 to modem 106b, as signal 110 may also be received by modem 106c, as seen in FIG. 1. Modem 106b may demodulate signal 110 to recover data 108.
A conventional twisted pair network—such as network 114—generally requires adherence to a rigid bus topology in order to minimize bus reflections and insure proper impedance matching, for example, at terminations 118, to insure good bus performance. A failure to comply with the bus topology requirements can result in reduced performance of bus 116 and network 114. Additional wiring—such as wiring 112—may also be needed for the sole purpose of satisfying the bus topology constraints.
Avionics system 100 may also include a power line network 120 for providing power to the avionics units 102. Power line network 120 may supply 28 Volt direct current (VDC) power 121, for example, to local power supplies 122a–122c. Each local power supply 122 may provide power 124 to modems 106a–106c and may provide power 126 to avionics host electronics 104a–104c. For example, each local power supply 122 may typically supply power at 1.5 VDC, 3.3 VDC, 5.0 VDC, or combinations of voltages.
FIG. 2 shows an example of a prior art alternating current (AC) power line modem 200 that may be used to provide digital communications over a power line, also referred to as power line networking. Power line modem 200 may be used to provide power line networking, for example, over 115 VAC wiring—such as common household or building wiring. Power line networking is currently being used, for example, to provide Internet access to homes through community power grids. As seen in FIG. 2, for example, 115 VAC power may be provided over power line 202, which may comprise a “hot” side 202a and a “neutral” or ground side 202b, to a local power supply 204. Local power supply 204 may provide direct current power 206 to modem 208. Local power supply 204 may also provide direct current power 210 at power outputs 212 for powering other equipment, such as a personal computer (not shown), for example. Local power supply 204 may typically supply power 206 and 210 at 1.5 VDC, 3.3 VDC, 5.0 VDC, or combinations of voltages.
A data signal 214 may also be transmitted or received over power line 202. Data signal 214 may be coupled to modem 208 through transformer 216. Transformer 216 may be a balun transformer for proper impedance matching and minimization of signal losses. Modem 208 may modulate data signal 214 with data 218 to produce and transmit data signal 214 or modem 208 may receive data signal 214 and demodulate data signal 214 to recover data 218. Communications protocols, such as Ethernet, may be used to allow multiple users (i.e., nodes) to share the network bus, i.e., power line 202. Data signal 214 may be modulated, for example, using techniques such as PCM, PSK, or FSK, as described above. Thus, power line 202 may be used for both power transmission and for data transmission as a network bus.
As seen in the example presented in FIG. 2, use of power transmission lines for data communications can eliminate the need for separate data communications lines, such as the data quality wiring 112 of network 114 seen in FIG. 1. By eliminating redundant wiring in an avionics system in an aircraft or spacecraft, such as wiring 112 in avionics system 100, significant weight savings can be achieved for the aircraft or spacecraft. Weight is a design constraint of any air or space vehicle. Reducing the number of wires used by the avionics reduces the weight of an air vehicle, enhancing the performance and capabilities of the vehicle. The transformer coupling of data signals to power lines—for example, the coupling of data signal 214 to modem 208 shown in FIG. 2—is not appropriate, however, for use with direct current power systems such as the 28 VDC power systems typically found in aircraft and used to power avionics systems, such avionics system 100 shown in FIG. 1. The transformer coupling using transformer 216, for example, is not appropriate because the primary winding of transformer 216, as shown in FIG. 2, wired from “hot” side 202a across power line 202 to “neutral” or ground side 202b, would short out local power supply 204 if direct current were being used.
As can be seen, there is a need for communication over power lines in order to share a single wire that simultaneously provides both direct current power and digital communications for avionics and control systems in airborne vehicles and spacecraft. Also there is a need for reduction, through communication over power lines, of the amount of wiring used by avionics and control systems in aircraft and spacecraft to reduce weight and save space inside the aircraft or spacecraft.